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Error.prototype.toString()

The toString() method returns a string representing the specified Error object.

Syntax

toString()

Return value

A string representing the specified Error object.

Description

The Error object overrides the Object.prototype.toString() method inherited by all objects. Its semantics are as follows (assuming Object and String have their original values):

Error.prototype.toString = function () {
  if (typeof this !== 'object' || typeof this !== 'function') {
    throw new TypeError();
  }

  let name = this.name;
  name = name === undefined ? 'Error' : String(name);

  let msg = this.message;
  msg = msg === undefined ? '' : String(msg);

  if (name === '') {
    return msg;
  }
  if (msg === '') {
    return name;
  }

  return `${name}: ${msg}`;
};

Examples

Using toString()

const e1 = new Error('fatal error');
console.log(e1.toString()); // 'Error: fatal error'

const e2 = new Error('fatal error');
e2.name = undefined;
console.log(e2.toString()); // 'Error: fatal error'

const e3 = new Error('fatal error');
e3.name = '';
console.log(e3.toString()); // 'fatal error'

const e4 = new Error('fatal error');
e4.name = '';
e4.message = undefined;
console.log(e4.toString()); // ''

const e5 = new Error('fatal error');
e5.name = 'hello';
e5.message = undefined;
console.log(e5.toString()); // 'hello'

Specifications

Specification
ECMAScript Language Specification # sec-error.prototype.tostring

Browser compatibility

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	Deno	Node.js
`toString`	1	12	1	6	4	1	4.4	18	4	10.1	1	1.0	1.0	0.10.0